The growth hormone pST is native to swine and accounts for maturation of the animal, including increasing the growth rate and the lean to fat ratio. Endogenous amounts of pST are small; therefore, efforts have focused on the preparation of exogenous pST for use in large-scale agriculture.
One aspect of those efforts has been the determination of the complete amino acid sequence of pST. It has been found that pST is a single chain polypeptide of 191 amino acids with two cystine bridges linking residues 53-164 and 181-189, respectively (Abdel-Meguid, S.S., et al., Proc. Natl. Acad. Sci., 84, 6434-6437 (1987)).
Efforts have also been directed to the identification of peptides which consist of small portions of the amino acid sequence of somatotropin of various species with a view to enhancing the activity of these growth hormones. Published European Patent Application 137,234 describes the cleavage of a 7 kd fragment from the C-terminal end of human growth hormone (hGH). Mice were injected with the fragment; the mice then generated antibodies to the fragment. Those antibodies were administered to mice in combination with hGH. It was found that mice receiving hGH plus antibodies to the hGH fragment exhibited greater growth than those receiving hGH alone.
Published European patent application 284,406 describes the preparation of a fragment corresponding to amino acid residues 35-53 of pST. The pST fragment was administered to pigs and anti-pST antibodies were generated. A similar experiment was carried out with a fragment of bovine somatotropin (bST). In the latter case, the anti-bST antibodies so generated were then administered together with intact bST and were found to enhance the activity of bST.